SK285673B6 - Process for the manufacture of the catalyst consisting of a porous carrier covered with metallic palladium and gold - Google Patents

Abstract

A method is provided to manufacture a palladium-gold catalyst by separately impregnating and fixing the palladium and gold and reducing the fixed solids to free metal on a suitable support useful for vinyl acetate manufacture from ethylene and acetic acid.

Description

The invention relates to a novel process for the preparation of a catalyst suitable for the reaction of ethylene, oxygen and acetic acid in the gas phase to form vinyl acetate. DETAILED DESCRIPTION OF THE INVENTION The present invention is directed to a novel process for preparing a catalyst useful in a catalytic process for the production of vinyl acetate, wherein the catalyst comprises palladium metal and gold deposited on a suitable porous support. This application is a continuation of USSN 08/823 592 of 25 March 1997, now withdrawn, which is a continuation of USSN 08/489 541 of 12 June 1995, which is a continuation of USSN 08/200 137 of 22 February 1994, called off.

BACKGROUND OF THE INVENTION

It is known in the art that vinyl acetate can be produced by reacting ethylene, oxygen and acetic acid in the gas phase and in the presence of a catalyst comprising palladium, gold and an alkali metal acetate deposited on certain support materials such as silica. In general, such a catalyst system has a high efficiency. Unfortunately, the results are not consistent with the use of these palladium and gold catalysts. Inconsistency seems to be based somewhere in the distribution of the composition or profile of the catalyst components that are deposited on and in the carrier. For example, using known vinyl acetate catalyst systems consisting of a porous support with palladium and gold, the deposited metal components in or on inner surfaces or central areas do not contribute significantly to the reaction mechanism, since the reactants are not readily capable of diffusing into the central or internal areas of the catalyst pores network. . The reaction therefore takes place essentially only on the outer or surface regions of the catalyst. The catalyst components in the internal regions of the support do not contribute much to the reaction scheme, thereby reducing the catalytic efficiency, expressed per unit weight of catalyst components. The use of highly active catalysts sometimes causes side reactions, resulting in reduced selectivity with respect to vinyl acetate.

Several patents have been granted, based on the required to even more uniform distribution and anchoring of the gold and palladium catalyst components in a narrow strip on the surface of the support to give a vinyl acetate catalyst providing high yields, good selectivity and long life. Examples of such patents include U.S. Patent 5,274,181, 4,087,622, 4,048,096, 3,822,308, 3,775,342, and British Patent 1,521,652. Some US patents from Hoechst Celanese Corporation Nos. 5,314,858 and 5,332,710 and their PCTs and foreign counterparts, including U.S. Patent No. 5,691,267 (WO 97/28 790), describe and claim improvements in the technology base.

A basic process for forming a palladium and gold vinyl acetate catalyst deposited on a catalyst support comprises (1) impregnating the support with aqueous solutions of water-soluble palladium and gold compounds, (2) precipitating the water insoluble palladium and gold compounds on the catalyst support by introducing the impregnated catalyst support into by contacting a solution of compounds capable of reacting with water-soluble palladium and gold compounds to form insoluble noble metal compounds, (3) washing the treated catalyst with water to remove the anions released from the original palladium and gold compounds upon precipitation; and (4) conversion. water-insoluble palladium and gold compounds on the free metals by the action of a reducing agent. The final treatment typically comprises (5) impregnating the reduced catalyst with an aqueous alkali metal acetate solution and (6) drying to the final catalyst product.

Existing efforts to create a uniform (uniform) distribution of palladium metal and gold metal on a support have included some modifications to the above manufacturing steps and / or the use of support materials with different specified pore dimensions.

U.S. Patent 5,314,858 relates to a process comprising (1) simultaneous or sequential impregnation of a catalyst support with aqueous palladium and gold salt solutions such as palladium-sodium chloride and gold chloride solutions, (2) precious metal fixation on the support by precipitation of water-insoluble compounds palladium and gold by the action of a reactive basic solution, such as an aqueous sodium hydroxide solution, on the impregnated carrier; the reaction produces palladium and gold hydroxides on the support surface, (3) washing with water to remove chloride ions (or other anions), and (4) reducing the noble metal hydroxides to free palladium and gold, wherein the improvement involves the use of two separate precipitation steps in which the amount of reactive compound in contact with the salt impregnated with the carrier in each precipitation step is not higher than the amount necessary to react with the noble metal compound (water-soluble) in the impregnated in the carrier. Between the individual precipitation or fixation steps, the carrier impregnated with the reactive basic solution is allowed a specified time to allow precipitation of the water-insoluble noble metal compounds before the second fixation step, in which an additional amount of reactive basic compound is added to the carrier.

SUMMARY OF THE INVENTION

SUMMARY OF THE INVENTION The present invention provides a process for preparing a palladium and gold vinyl acetate catalyst on a porous support wherein fixation of water-soluble noble metal compounds in the form of water-insoluble compounds can be achieved on the support by impregnated support with sufficient reactive compound to ensure complete precipitation and fixation noble metal compounds on a carrier in multiple fixation steps.

It has now been found that exceptionally active supported catalysts containing palladium and gold and suitable for the production of vinyl esters from ethylene, lower C 2 -C 4 carboxylic acids and gas phase oxygen at elevated temperatures and at normal or elevated pressure can be prepared by adjusting the production process. of steps (I) and (2) of the method described. Typically, in the precipitation step (2), the impregnated catalyst support was impregnated with one or more reactive compound solutions, causing both metals to precipitate simultaneously in the form of hydroxide (oxide), at such time as necessary to completely eliminate the insoluble noble metal compounds. During a typical prior art precipitation step, the inventors have noted that palladium precipitates are precipitated at a higher rate than gold precipitates and that increased amounts of non-precipitated gold can be leached from the catalyst support before the catalyst support is immobilized by precipitation or can be leached from the catalyst support. the carrier in the washing step. This is why the palladium / gold ratio varies from impregnation to precipitation. Although this problem exists in precipitation solutions whose volume is equal to the pore volume of the support, this problem is even more serious when precipitation is carried out by dipping the impregnated carriers into dilute precipitation solutions.

To overcome this problem and in accordance with the present invention, a suitable catalyst has been prepared by a process comprising (1) impermeable impregnation of the catalyst support with aqueous solutions of palladium and gold salts such as palladium sodium chloride and gold chloride, (2) impermeable fixation of both noble metals water-insoluble palladium and gold compounds by treating the impregnated carrier with a reactive basic solution, such as aqueous sodium hydroxide, which reacts to form palladium and gold hydroxides on the surface of the catalyst, (3) washing with water to remove chloride ions (or other anions); reduction of noble metal hydroxides to free (metal) palladium and gold.

In the process for preparing the improved catalyst of the present invention, a suitable catalyst support is first impregnated with an aqueous solution containing or a water-soluble palladium compound or a water-soluble gold compound. Palladium (II) chloride, palladium (II) chloride and palladium (II) nitrate are examples of suitable water-soluble palladium salts, and as water-soluble gold compounds, gold chloride or tetrachlorolatic acid and its alkali metal salts can be used. Commonly available tetrachlorolatic acid and palladium sodium chloride are preferred because they have high water solubility. An amount of these compounds is used to provide 1 to 10 g of palladium and 0.5 to 5 g of gold per liter of finished catalyst. Accordingly, the amount of gold present in the catalyst will be from about 10 to about 70% of the amount of palladium. A catalyst for producing vinyl acetate from ethylene, oxygen and acetic acid can be prepared by the process of the present invention such that it contains at least 17% more palladium and at least 12% more gold than in the process of US 5,332,710. a catalyst having at least the same or greater amount of gold than using the preparation process of U.S. Pat. No. 5,314,858.

Comparative examples were made with the catalysts prepared according to the process of the present invention (separate fixation technique) as described herein and the double fixation preparation process of U.S. Pat. No. 5,314,858. The results of these experiments are shown in Tab. 2. It is apparent from the results that the method of the present invention achieves higher gold capture than the method of the US '858 patent.

An important is the volume of the noble metal solution used to impregnate the support. For effective deposition, the volume of impregnating solution should be 95-100% of the absorptive capacity (dry absorption capacity) of the catalyst support; the preferred volume will be 98 to 99% of the absorbency of the carrier.

The catalyst support material of the invention may be in any geometric shape. For example, the carrier may have a spherical shape, a tablet or a roller. The geometric dimensions of the support may generally be in the range of 1 to 8 mm. The most suitable geometric shape is spherical, for example, balls with diameters ranging from 4 to 8 mm. Such carriers are generally called pills.

The specific surface of the carrier may vary within wide limits. Suitable as such carrier materials, having a surface area (inside) from 50 to 300 m ² .g ^-1 and especially 100-200 m ² .g '(measured by the BET method).

Examples of carrier materials that can be used include silica, alumina, aluminosilicates or spinels. The preferred carrier material is silica.

After each impregnation of the carrier with a water-soluble palladium or gold salt, the impregnated carrier may be dried before the palladium or gold compounds are fixed in the form of water-insoluble compounds on the carrier. The fixing solution is one which is basic, for example an aqueous solution containing alkali metal hydroxides, alkali metal bicarbonates and / or alkali metal carbonates. Highly preferred are aqueous solutions of sodium hydroxide or potassium hydroxide. By treatment with a basic solution, the noble metal salts are converted into water-insoluble compounds believed to be hydroxides and / or oxides, at least when the basic solution is a sodium hydroxide or potassium hydroxide solution.

According to the prior art, the basic fixative solution is dispersed on the impregnated carriers, and the carriers thus treated are allowed to stand for up to 24 hours or longer for precipitation. The volume of the fixation solution is equal to the dry absorptivity of the support and the amount of basic compound used is in excess (on a molar basis) relative to the amount required for said reaction with the entire amount of impregnated noble metal salts.

In the method of the invention, the amount of basic compound in the fixation solution in each fixation step should be such that the ratio of alkali metal to anion of the water-soluble noble metal salt is from 1: 1 to 1.8: 1 (mole).

The volume of solution in each fixation step may be equal to the pore volume of the carrier, or the impregnated carrier may be completely immersed in the fixation solution, the total volume of the solution being sufficient to embed the carrier. Optionally, the support may be impregnated in one or both separate fixation steps in a manner termed "rotation immersion" as disclosed in U.S. Patent 5,332,710. In this process, the impregnated catalyst support is immersed in a basic fixative solution and rolled. is rotated or rotated therein, at least during the first stage of the precipitation of water-insoluble noble metal compounds. Rotation or rewinding of the carriers in the basic fixative solution should take place for at least 0.5 hours after the first soaking, preferably for at least 2.5 hours. Diving with motion may take up to 4 hours; in order to ensure complete precipitation of the water-soluble noble metal compounds, the carriers can be allowed to stand in the fixative solution.

Since the precise category of the immersion device in motion is not critical, any type of rotary or rocking device may be used. What may be decisive is the rate of rotational movement. The movement must be sufficient to ensure that the entire surfaces of the impregnated carriers are evenly in contact with the basic fixing solution. However, the rotation should not be so careful that the insoluble noble metal compounds are abraded from the support surface. Generally, the device is to be rotated at about 1 to 50 rpm and possibly even higher, depending on the particular carrier used and the amount of noble metal deposited on the carrier. The rotational speed to be used is variable and may also depend on the device used, the size and shape of the support, the type of support, the proportional metal content of the support, and the like, but should be within this range, although there may be little image rubbing; however, it does not occur that the insoluble compounds are abraded to an unacceptable extent from the surface of the carrier.

Prior to each fixing step, the impregnated catalyst support may be dried to remove entrapped water. If the fixation is performed according to the pore volume method, drying is then required to achieve complete contact of the noble metal compound with the fixing solution causing precipitation. An advantage of the immersion process is that the impregnated carrier is not dried prior to fixation.

Optionally, the impregnating solution containing the gold compound and the fixative solution may be mixed together just prior to impregnation, omitting a separate fixation step. This treatment is possible since, at ambient temperature, the insoluble gold salt is formed quite slowly.

After fixation, the carriers are washed, for example with distilled water, to remove anions, for example chlorides, that come from the first impregnating solution and are still present on the carrier. Washing is continued until all anions have been removed from the support. Ideally, no more than 1000 ppm anions should remain on the support. In order to ensure substantially complete removal of anions such as chloride ions from the catalyst, the wash liquid may be tested for the presence of silver nitrate chlorides. Then, the catalyst is dried at a temperature not exceeding about 150 ° C.

The fixed and washed material is then treated by reduction to convert the salts and noble metal compounds present to the metal form. The reduction can be carried out in the liquid phase, for example in an aqueous medium with hydrazine hydrate, or in the gas phase, with hydrogen or hydrocarbons, for example ethylene. If the reduction is carried out with a hydrazine hydrate solution, the reaction is preferably carried out at ambient temperature. If the reduction is carried out in the gas phase, it may be advantageous to carry out the reduction at elevated temperatures, for example at 100 to 200 ° C in the case of ethylene reduction. The reducing agent is used in an appropriate excess to ensure that the entire amount of the noble metal salts and compounds has been converted to the metal form.

Depending on the purpose for which the catalyst is prepared in this way, it can be treated with the usual additives. Thus, for example, the addition of alkali metal acetates is advantageous when the catalyst is to be used to prepare unsaturated esters from olefins, oxygen and organic acids. In this case, the catalyst can be impregnated with an aqueous potassium acetate solution and then dried.

The catalyst according to the invention can be used particularly advantageously in the preparation of vinyl acetate from ethylene, oxygen and acetic acid in the gas phase. Catalysts according to the invention which contain silicon dioxide and alkali metal acetate additives as carrier material are very suitable for this purpose. In the preparation of vinyl acetate, such catalysts are also characterized by high efficiency, selectivity and durability.

DETAILED DESCRIPTION OF THE INVENTION

Examples 1 to 4

The catalysts in Examples 1-4 were prepared by the process of the invention. Individual examples are given in Tab. 1. In each example, a catalyst support from a catalyst was used

The Chemistry Court, having a spherical shape and a diameter of approximately 7.3 mm, unless otherwise stated. In all examples, 250 ml of the support was impregnated with an aqueous solution containing an amount of palladium sodium chloride sufficient to give 1.65 g (6.6 g of T ¹ ) palladium on the support. In tab. 1, the term "incipient wetness" means in the art a volume of solution equal to the pore volume of the carrier. The treated carrier is then fixed with an aqueous sodium hydroxide solution as described in Tab. In the first fixation step, the amount of sodium hydroxide used was determined by the molar ratio of sodium cation to chloride anion of 1.2: 1. 1, different fixation times are also reported. After the first fixation, the treated material was thoroughly washed with distilled water to remove the chloride ions. Unless otherwise indicated, the flow of wash water was 200 mih ^'1 for about five hours. After washing, the catalysts were air dried at 100 ° C for 1 hour. The dried catalysts were then impregnated with 0.75 g (3.0 g / ^l ) of gold used as an aqueous solution of sodium chlorolatite. After impregnation, the carriers were fixed with an aqueous sodium hydroxide solution as shown in Tab. The amount of sodium hydroxide in the second fixation step was determined as the molar ratio of sodium to chloride anion of 1.2: 1. different fixation times are also reported. 1. After the second fixation, the base treated material was thoroughly washed with distilled water to remove chloride ions. Unless otherwise stated, the wash water flow rate was 200 ml.h ^-1 for approximately five hours. After washing, the catalysts were dried at 150 ° C under a nitrogen atmosphere. Each of the prepared catalysts was then reduced with ethylene gas at 150 ° C. The reducing gas contained 5% ethylene in nitrogen and passed over the catalysts for 5 hours at atmospheric pressure. The reduced catalyst was impregnated with an aqueous solution containing 10 grams (40 g.l ^-1 ) of potassium acetate in a volume of solution such as that of the carrier. Then the catalysts were dried at temperatures not higher than 150 ° C.

The catalysts in Examples 4 to 6 were prepared as described in U.S. Patent 5,314,858. The catalysts in Examples 7 to 11 were prepared by the process of the present invention. The initial and final specific metal content of the catalysts is shown in Table 2. It is evident that the average metal capture for Pd according to the US '858 patent procedure was 88% and for Au was 77%, while the average metal capture for Pd according to the inventive method was 88% and for Au was 85%. The catalysts in Examples 1-11 were used to prepare vinyl acetate by reacting ethylene, oxygen and acetic acid by methods well known in the art.

Table 1

process Example 1 Example 2 Example 3 Example 4 Pd immersion, drying beginning wet, without drying beginning wet, without drying beginning wet, without drying starting moisture, drying at 100 ° C, 1 h Fixation Pd By immersion in motion, 2.5 h, 1.2: l = Na: Cl By immersion in motion, 2.5 h, 1.2: 1 = Na: Cl Dip, 16 h, 1.2: 1 = Na: Cl By immersion in motion, 16 h, 1.2: 1 = Na: CI First wash 5h 5h 5h 5h First drying Mp 100 ° C 100 “C Mp 100 ° C 100 ° c Au impregnation, drying starting moisture, drying 100 ° C, 1 h The impregnated and fixative solution was stirred for 16 h without drying starting moisture, drying 100 ° C, 1 h starting moisture, drying 100 ° C, 1 h Fixation Au starting wet, 16 h, 1,2: 1 = Na: Cl ON THE. starting wet, 16 h, 1.2: 1 = Na: CI starting wet, 16 h, 1,2: 1 = Na: Cl Second wash 5 h 9 h 5h 5h Second drying 150 ° C in a stream of nitrogen, 14 h 150 ° C in a stream of nitrogen, 14 h 150 ° C in a stream of nitrogen, 14 h 150 ° C in a stream of nitrogen, 14 h

Tab. 2 Comparative Examples; the method according to the invention used (separate fixation, examples 7 to 11) and the method according to the invention US 5 314 858 with double fixation (examples 4 to 6)

Initial specific metal content Final specific metal content Metal yield process Example Au g.ľ ^{1 1} g · l Pd Au g.ľ ^{1 1} g · l Pd % Au % Pd Double fixation 4 3.30 7.0 2.58 6.05 78 86 5 3.25 6.90 2.35 6.06 72 88 6 3.45 7.31 2.77 6.57 80 90 average 77 88 Separate fixation 7 3.73 7.00 3.14 6.10 84 87 8 3.73 7.00 3.25 5.91 87 84 9 4.00 7.00 3.28 6.02 82 86 10 4.30 7.50 3.75 6.76 87 90 11 4.00 7.00 3.47 6.42 87 92 average 85 88

PATENT CLAIMS

Claims (11)

A process for the preparation of a porous support catalyst comprising palladium metal and gold, which comprises impregnating said support with water-soluble noble metal compounds in a step of fixing the conversion of the water-soluble noble metal compounds absorbed into water-insoluble noble metal compounds contacting the impregnated carrier with a solution comprising a compound that reacts with the water-soluble noble metal compounds to precipitate water-insoluble noble metal compounds on the carrier, further comprising reducing the water-insoluble noble metal compounds on the carrier with a reducing gas beyond forming a free metal comprising the steps of: (1) contacting the carriers with one of said water-soluble compounds of said noble metals to impregnate the carrier with a water-soluble compound; (2) converting said water-soluble compound. the noble metal compound in the first fixation step to the water-insoluble noble metal compound by contacting the impregnated carrier with a solution comprising a compound that reacts with said water-soluble compound so as to precipitate a water-insoluble noble metal compound on the carrier, ( 3) contacting the once impregnated and fixed support with the second of said water-soluble noble metal compounds to impregnate the carrier with said water-soluble compound, (4) converting the second, water-soluble noble metal compound in a second fixing step into water insoluble noble metal compound by contacting the impregnated carrier with a second solution comprising a compound that reacts with a second water-soluble compound such that a water-insoluble second noble metal compound precipitates on the carrier and then a reduction of the water-insoluble noble metal compounds to reduction carriers gas to form free metals. 2. The process of claim 1 wherein the compound that reacts in the first and second fixing steps is a basic compound. The process according to claim 2, wherein the basic compound is potassium hydroxide or sodium hydroxide. 4. The method of claim 1, wherein the volume of the solution of the reacting compound coming into contact with the impregnated carrier in the first fixation step is equal to the dry absorptivity of the carrier. 5. The method of claim 1, wherein the volume of the solution coming into contact with the impregnated carrier in the first fixation step is sufficient to immerse the carrier. The method of claim 1, wherein the volume of the solution of the reacting compound coming into contact with the impregnated carrier in the second fixation step is equal to the dry absorptivity of the carrier. 7. The method of claim 1 wherein the volume of the solution coming into contact with the impregnated carrier in the second fixing step is sufficient to immerse the carrier. Method according to claim 5, characterized in that the first fixing step is carried out by rotating immersion immersion. The method of claim 8, wherein the noble metal compound that first comes into contact with the carrier and is subjected to a first fixation step is a Pd compound. The method of claim 1, wherein the individual steps are as follows: (1) contacting the water-soluble compound Pd solution with the porous carrier to impregnate the carrier with the water-soluble compound Pd solution; (2) converting the water-soluble compound Pd in the first fixation step to a compound Pd that is water-insoluble by contacting the carrier Pd compound with a basic compound, immersing the carrier in a solution of the basic compound and rolling, at least in the early stages of precipitation water insoluble Pd compound; (3) for impregnating the carrier with a water-soluble gold compound, the impregnated and fixed carrier is once contacted with the water-soluble gold compound; (4) converting the water-soluble Au compound on the carrier to a water-insoluble Au compound by contacting the Au compound on the carrier with a basic compound in a second fixation step, wherein the impregnated carrier and the basic compound solution are contacted until the initial and (5) reducing the Pd and Au compounds with a reducing agent to form the free metals Pd and Au on the support. The method of claim 1, wherein the steps are as follows: (1) contacting the water-soluble compound Pd with a porous carrier to impregnate the carrier with the water-soluble compound Pd; (2) converting the water-soluble compound Pd in the first fixation step to a compound Pd that is water-insoluble by contacting the carrier Pd compound with a basic compound, immersing the carrier in a solution of the basic compound and rolling, at least in the early stages of precipitation water insoluble Pd compound; (3) contacting the once impregnated and fixed carrier with a water-soluble gold compound and a basic compound solution such that impregnation of the carrier with a water-soluble Au compound is carried out simultaneously with the second fixing step; and (4) reducing the Pd and Au compounds with a reagent to form the free metals Pd and Au on the support.